Semiconductor processing

ABSTRACT

Semiconductor processing and equipment are disclosed. The semiconductor equipment and processing provide semiconductor wafers with reduced defects.

The present invention is directed to semiconductor wafer processing toprovide semiconductor wafers having reduced defects. More specifically,the present invention is directed to semiconductor wafer processing toprovide semiconductor wafers having reduced defects processed in waferholding articles with reduced surface roughness.

One of the problems associated with processing semiconductor wafers isthat the wafers typically form defects known as slip. Slip is adislocation of molecules along crystallographic planes formed when partsof a single crystal move relative to each other along these planes. Thismovement may occur when there is less than optimum contact betweensusceptors and wafers. Typically, the slip originates on the backside ofthe wafer which is in contact with a susceptor surface and thenpropagates through the wafer during continued processing. There can bemany causes of slip, but a fundamental problem is small area (sharppoint) contact on the surface that causes a high localized stress whenthe wafer is placed on a surface or moves on a surface. Thus, it isimportant to produce a surface that is free of sharp objects orprotrusions and to provide edges that are rounded. The less than optimumcontact is often due to the rough surface topography of the ceramicmaterial from which the susceptor is made. This movement also may occurwhen the wafer is unevenly heated or cooled during the film formingprocess, particularly between the top and bottom surfaces of the waferand at the outer edges where heat is dissipated quicker. Thermal stressis then produced at portions of the wafer where large temperaturegradients exist, causing slip when parts of the crystal move to relievesuch stress. Wafers having slip defects can lead to undesirable yieldloss when used to fabricate semiconductor devices.

Crystallographic slip may, to some degree, be reduced by maintainingideal contact between the wafers and the wafer susceptors, by heatingthe wafers very slowly, or by making the wafers thicker or smaller indiameter than present conventional wafers. However, such techniques aredifficult to implement and utilize in production environments.

One attempt to address the problem of slip is disclosed in U.S. Pat. No.6,099,650 to Carbonaro et al. Carbonaro addresses the problem of slip byplacing a cover over the wafers held in a susceptor in a chemical vapordeposition reactor. According to Carbonaro the cover serves as a heatbarrier to radiate and reflect heat from the susceptor onto the wafers.This allegedly prevents heat from being radiated from the wafers, andthe temperature gradient across the wafers is reduced, thereby reducingor eliminating slip in the wafers during and after the formation ofepitaxial layers. The cover has the same shape and diameter of thesusceptor and is composed of graphite with a silicon carbide coating of0.6 cm to 2.54 cm thick. Varying the thickness allegedly enablescontrolling the amount of heat radiated from the cover. The cover isplaced 0.6 cm to 5 cm above the wafers. Adjusting the distance allegedlyenables controlling the amount of heat reflected back on the wafers.This is believed to increase the heat on top of the wafers.

In addition to slip, other problems associated with semiconductorprocessing include sticktion and float. Sticktion is sticking of thewafer to the susceptor or other wafer holding apparatus. Sticktion isdifficult to measure quantitatively, but qualitatively you may notice itwhen the wafer is lifted from the susceptor. If you experience stickingwith stress damage to the wafer, then sticktion is present. Stressdamage is observable by crystalline point defects, line defects andfractures in the wafer. Float occurs when the wafer is supported on afew high points on the susceptor surface and trapped gases pass betweenthe susceptor surface and the wafer causing the wafer to move relativeto the susceptor. Ideally, both sticktion and float are zero duringsemiconductor wafer processing and the wafers remain motionless in theirholding apparatus. Accordingly, there is a need for improved methodswhich address the problems discussed above.

In one aspect of the invention there is provided a method includingmodifying one or more surfaces of a wafer holding article to provide awafer holding article having a surface of Ra of less than or equal to 3microns and an Rz(din) of less than or equal to 15 microns; placing oneor more semiconductor wafers in the wafer holding article; placing thewafer holding article having the surface of Ra of less than or equal to3 microns and an Rz(din) of less than or equal to 15 microns with theone or more semiconductor wafers in a processing chamber; and processingthe one or more semiconductor wafers to modify the one or moresemiconductor wafers to form a modified semiconductor wafer having lessthan or equal to 50 slip defects.

In another aspect there is provided a method including modifying one ormore surfaces of a wafer holding article to provide a wafer holdingarticle having an edge radius of 0.05 mm or more, an Ra of less than orequal to 3 microns and an Rz(din) of less than or equal to 15 microns;placing one or more wafers in the modified wafer holding article;placing the modified wafer holding article having the Ra of less than orequal to 3 microns and an Rz(din) of less than or equal to 15 micronswith the one or more semiconductor wafers in a processing chamber; andprocessing the one or more semiconductor wafers to modify the one ormore semiconductor wafers to form a modified semiconductor wafer havingless than or equal to 50 slip defects.

In a further aspect a wafer holding article is provided having an Ra ofless than or equal to 3 microns and an Rz(din) of less than of equal to15 microns. The wafer holding article also may have an edge radius of0.05 mm or more.

In addition to eliminating or reducing slip, the methods reduce oreliminate the imbalance between sticktion and float.

FIG. 1 is a perspective view with partial cut-away showing a susceptorring;

FIG. 2 is a cross-sectional side view of the susceptor and wafer of FIG.2;

FIG. 3 is a cross-sectional side view of the rounded edges of thesusceptor; and

FIG. 4 is a photograph at 30× of machined and lapped silicon carbidesurfaces.

As used throughout this specification, the following abbreviations shallhave the following meanings, unless the context indicates otherwise: °C.=degrees Centigrade; μm=microns=micrometers; m=meters; cm=centimeter;mm=millimeters; nm=nanometers; A=amperes; mA=milliamperes; CVD=chemicalvapor deposition; PVD=physical vapor deposition; ml=milliliters;min=minute; sec=second; msec=millisecond; hr=hour; Hz=hertz;kHz=kilohertz; W=watt=1 joule/second; erg=1 dyne cm=10⁻⁷ Joules;mV=millivolts; 1 atmosphere=760 torr; 1 atmosphere=1.01325×10⁶dynes/cm²; psi=pounds per square inch; 1 atmosphere=14.7 psi;rpm=revolutions per minute; Å=angstroms=1×10⁻⁴ microns; RMS=root meansquare; and SEM=scanning electron microscopy.

All percentages are by weight unless otherwise noted. All numericalranges are inclusive and combinable in any order, except where it islogical that such numerical ranges are constrained to add up to 100%.

Methods include modifying one or more surfaces of a wafer holdingarticle to provide a wafer holding article having a surface of Ra ofless than or equal to 3 microns and an Rz(din) of less than or equal to15 microns; placing one or more semiconductor wafers in the waferholding article; placing the wafer holding article having the surface ofRa of less than or equal to 3 microns and an Rz(din) of less than orequal to 15 microns with the one or more semiconductor wafers in aprocessing chamber; and processing the one or more semiconductor wafersto modify the one or more semiconductor wafers to form a modifiedsemiconductor wafer having less than or equal to 50 slip defects.

In addition to providing reduced slip defects, processing semiconductorsin wafer holding apparatus having a surface of Ra less than or equal to3 microns and an Rz(din) of less than or equal to 15 microns reduces oreliminates the imbalance between sticktion and float.

The roughness of a surface consists of finer irregularities of surfacetexture and includes Ra and Rz(din). “Ra” refers to the arithmeticaverage of the absolute values of the profile (peak) height deviationsfrom a mean line recorded within a certain evaluation length (averageroughness). Ra ranges from 3 microns or less, or such as from 0.1microns to 0.001 microns, or such as from 0.01 microns to 0.005 microns.Rz(din) value is the average maximum peak-to-valley height of any fiveconsecutive sampling lengths within the measurement length. Thepeak-to-valley distance is the distance between the height of a surfacefeature and a trough or valley in the surface. A “peak” is the point ofmaximum height on a given portion of the profile that lies above acenterline. A “valley” is a point of maximum depth on a given portion ora profile that lies below a centerline. Rz(din) ranges from 15 micronsor less, or such as from 1 micron to 0.005 microns, or such as from 3microns to 0.05 microns.

A variety of methods may be used to measure the roughness of a surface.One suitable method is an autocovariance function. The two-dimensionalautocovariance function is a function of direction and distance andrepresents the expected value of the height product of all two-pointpairs that are separated by certain length in a direction. In otherwords, the auto covariance function describes the characteristic featurelength, i.e. the length between two peaks having a certain height. For adescription of the application of an autocovariance function to thedetermination of surface topography, see Kiely et al., Quantification ofTopographic Structure by Scanning Probe Microscopy, Journal of VacuumScience Technology B, vol. 15, no. 4, July/August 1997, pp 1483-1493.Further descriptions of roughness parameters and methods of determiningthe values of these parameters are provided in Standard ASME B46.1-2002,Surface texture (Surface Roughness, Wavines and Lay), American Societyof Mechanical Engineers, 2003. Typically, the directionality surfacetopography of the surface features are determined using atomic forcespectroscopy (AFM) or an optical profilometer.

The wafer holding articles also may have wafer support edges with anedge radius of 0.05 mm or more, or such as from 0.1 mm to 1 mm. Theradius is measured from the quarter of the circle, which is aconventional method used in the art. A profilometer may be used tomeasure the radius or it may be done using a microscope. An edge radiusof 0.05 mm or more also reduces or eliminates crystalline point defects,line defects as well as fractures in the wafer caused by stress.

Any suitable ceramic may be used to make the wafer holding articles.Typically, the material used to make the wafer holding articles issilicon carbide. Silicon carbide may be made by many different methodsresulting in silicon carbides having different and distinct propertiessuch as thermal conductivity, electrical resistivity, density andcrystalline structure. Silicon carbide may be single crystal orpolycrystalline. Silicon carbides include, but are not limited to,chemical vapor deposited silicon carbide, physical vapor depositedsilicon carbide, reaction bonded silicon carbide, sintered siliconcarbide, hot pressed silicon carbide and foamed silicon carbide.Typically, the silicon carbide is chosen from CVD silicon carbide, PVDsilicon carbide, sintered silicon carbide and hot pressed siliconcarbide. More typically, the silicon carbide is chosen from CVD siliconcarbide and PVD silicon carbide. Most typically, the silicon carbide isCVD silicon carbide. The CVD silicon carbide typically is β-cubicsilicon carbide.

Any suitable method may be used to modify the surface of the ceramicarticles as long as the method provides the desired surface roughnessand edge radius. Such methods include, but are no limited to, machining,lapping, polishing, grinding, grit blasting, carbon dioxide blasting,etching, such as wet etching with acids and bases or plasma etching,ablation such as energetic ablation, oxidation, electric dischargemachining, direct CVD, or forming coatings on the articles, such as byCVD, PVD and energy assisted CVD and PVD. Such coatings include, but arenot limited to silicon nitride, silicon, silicon carbide, silicondioxide or carbon. Combinations of the foregoing methods also may beused to provide the desired surface. Typically, the surfaces of thesilicon carbide wafer holding article are smoothed using lapping,polishing, or oxidation. More typically, the surfaces of the siliconcarbide wafer holding article are smoothed by oxidation to form asilicon dioxide layer on the silicon carbide followed by stripping withacid.

Typically the ceramic article is first machined. In general, machiningmacroscopically removes undesired surface features of the ceramicarticles after they are formed such as, for example, by CVD or PVD, andshapes the articles for their desired functions. Conventional machiningprocess may be used. Such processes include, but are not limited to,grinding, lapping, honing, ultrasonic machining, water jet or abrasivemachining, laser machining, electrical discharge machining, ion beammachining, electron beam machining, chemical machining andelectrochemical machining.

The processes of machining and smoothing the surface to provide thedesired Ra and Rz(din) as well as the desired edge radius may becombined. Surface smoothing methods such as wet etching, lapping,polishing, grinding, electric discharge, laser ablation, e-beamablation, X-ray ablation, microwave ablation and radiation energyablation may be combined with machining. When the surface rougheningmethods are combined with the machining processes, minor experimentationmay be done to modify the process parameters of machining and themethods of roughening the surface to provide the desired article.

CVD is used after machining. Ceramic materials which may be formed byCVD include, but are not limited to, silicon carbide, silicon nitride,synthetic diamond, carbon, titanium boride, titanium carbide, boroncarbide, boron nitride and carbon nitride. Conventional depositionchambers and reactions precursors may be used. The deposition processesare performed in inert atmospheres such as argon, helium, neon, krypton,xenon, nitrogen and mixtures thereof. Flow rates for such inert gasesduring deposition are conventional. The deposition rates of theprecursors are less than 5 microns/min, or such as from 0.005microns/min to 1 micron/min. Such rates depend on the deposition chambertemperatures, pressures and flow rates or the precursors. Suchparameters may be adjusted during deposition to obtain the desireddeposition rates. For example, deposition chamber temperatures may rangefrom 1200° C. to 1700° C., or such as from 1250° C. to 1600° C.Deposition pressures range from 100 torr to 400 torr, or such as 125torr to 350 torr, or such as 150 torr to 250 torr. Conventionalprecursor flow rates may be used and varied during deposition to obtainthe desired deposition rates.

Energetic ablation uses radiant energy or beams of electromagnetic wavesor particles to modify the ceramic surface. Radiant energy ablation orheat treating typically is done in a conventional vacuum chamber. Avacuum is slowly created around the ceramic article. Pressures may rangefrom 10⁻⁴ to 10⁻¹⁰ torr, or such as from 10⁻⁶ to 10⁻⁸ torr. Pressure isheld constant while the ceramic is then ramped to temperatures of 1000°C. to 2000° C., or such as from 1200° C. to 1500° C. The ceramic articleis held at a constant temperature and pressure from 2 to 10 hours, orsuch as from 4 to 8 hours. The ceramic is then slowly cooled and broughtto atmospheric pressure and removed from the chamber. Cooling andpressure reduction is done over a period of 5 min to 60 min, or such asfrom 10 min to 30 min and leaving the ceramic in the chamber to cool toroom temperature over 6 hr to 48 hrs, or such as from 12 hr to 24 hr.

Electromagnetic waves or particles include, but are not limited to,protons, neutrons, electrons, X-rays, lasers (high intensity opticalradiation), electrical discharge machining (EDM), also known aselectrical arc, and microwaves. Apparatus used to modify the surfacegenerally includes a means for controlling and focusing a particularbeam of energy onto the surface of the ceramic. The particular meansemployed to control and focus the beam depends upon the particular typeof electromagnetic radiation used. Such apparatus are well known in theart.

In general, where an electromagnetic beam is generated by an electronbeam, ion beam or electrical arc an electrical current flows to thearticle. The current may range from 5 mA to 100 mA, or such as from 10mA to 80 mA. The energy delivered by the electromagnetic beam may bedefined in terms of a power density, which is the average power surfaceof the ceramic. Average power densities may range from 1000 W/cm² to5000 W/cm², or such as from 2000 W/cm² to 4000 W/cm² at a point on thesurface of the article upon which the beam is directed. The peak powerdensity of the electromagnetic beam may be from 5000 W/cm² to 10,000W/cm² or such as from 5500 W/cm² to 8000 W/cm² as a point on the surfaceof the ceramic. The peak power density may be defined as a processsetting where the bam is at its maximum focus (i.e. smallest spot size)at a given power setting. Dwell times for the electromagnetic beam mayrange from 0.1 msec to 5 msec, or such as from 0.5 msec to 2 msec.

Chemical treatments such as wet etching include the use of acids andbases to modify ceramic surfaces. Such acids include, but are notlimited to aqueous acid solutions such as sulfuric acid, nitric acid,hydrochloric acid, hydrofluoric acid, phosphoric acid and combinationsthereof. The concentrations of the acids used range from 20 wt % to 80wt %, or such as from 65 wt % to 70 wt %. When two or more acids aremixed together, equal amounts of each are typically used. Etching isdone for 30 min to 240 min, or such as from 60 min to 180 min. Etchingis done at temperatures of 20° C. to 100° C. or such as from 30° C. to85° C.

Bases include, but are not limited to, potassium hydroxide, sodiumhydroxide, ammonia hydroxide and combinations thereof. Concentratedforms of the bases are used. Typically, molten bases are used to etchthe article surfaces. Etching with molten bases involves temperatures of500° C. to 1000° C.

Dry etching or plasma etching involves generating plasma to energize ordissociate reactive gas species that interact with and remove materialfrom the surface of the ceramic. A plasma discharge is created bytransferring energy into a low-pressure gas. Dry etching may be done atplasma temperatures of 1000° C. to 5000° C., or such as from 1500° C. to3000° C. The article is typically at temperatures of 100° C. to 500° C.Energy sources include, but are not limited to, radio frequency energy,microwave energy and magnetic fields. Pressures typically range from10⁻³ torr to 10⁻¹⁰ torr, or such as from 10⁻⁵ torr to 10⁻⁸ torr. Varioustypes of plasma gases and mixtures may be used. Such gases include, butare not limited to, chlorine, fluorine, nitrogen trifluoride, hydrogenchloride, boron trichloride, sulfur hexafluoride, fluorocarbons, oxygenand inert gases such as argon, neon, krypton, helium and xenon. Etchingtime may range from 30 sec to 90 min, or such as from 60 sec to 60 min,or such as from 120 sec to 30 min.

Generally, one or more non-inert gases, such as chlorine, fluorine,nitrogen trifluoride, hydrogen chloride and oxygen, compose 10% to 50%by volume or such as 15% to 25% by volume of the plasma with theremainder one or more inert gases. Typically, etching is done withmixtures of chlorine, oxygen and one or more inert gases. Moretypically, etching is done with fluorine, oxygen and argon. The halogengases compose from 10% by volume to 30% by volume with oxygen composingfrom 10% by volume to 30% by volume with the remainder one or more inertgases. Etching is typically done for 60 sec to 3 hr, or such as from 15min to 2 hr, or such as from 30 min to 1 hr.

Another chemical treatment method used to modify silicon carbidesurfaces is oxidation. The silicon carbide article is placed in aconventional open air furnace at temperatures of 800° C. to 2000° C. orsuch as from 1000° C. to 1500° C. Heating continues for 100 hr to 400hr, or such as from 150 hr to 250 hr. To expedite the process additionaloxygen may be pumped into the furnace. Alternatively, the method may bedone in a closed furnace with oxygen pumped into the furnace. Typicallypressures in a closed furnace range from 50 torr to 1 atmosphere.Oxidation in closed furnaces typically takes from 5 hr to 30 hr, or suchas from 10 hr to 20 hr.

The silicon dioxide layer may range in thickness from 0.1 microns to 5microns or such as from 0.3 micron to 2 microns on the article. Thesilicon dioxide layer is then stripped off using a concentrated mineralacid solution. Suitable acids include, but are not limited to,hydrochloric acid, sulfuric acid, nitric acid, hydrofluoric acid,phosphoric acid and mixtures thereof. Typically hydrofluoric acid isused. Stripping is done at temperatures of 20° C. to 90° C.

When the silicon dioxide is removed, rough surface features and sharppeaks which the silicon dioxide coats, are removed as well. Removal ofthe silicon dioxide layer provides a smooth surface having the desiredsurface features.

Lapping and polishing may be done using conventional apparatus, such aswith various lapping apparatus and polishing pads. When lapping platesare used, the plates turn at surface speeds of 300 m/min to 3000 m/minor such as from 600 m/min to 2500 m/min. Lapping and polishing are doneat pressures of 1 psi to 15 psi, or such as from 1 hr to 10 hrs.

Lapping and polishing may be done with slurries, pastes and dryparticles. Various types of particles may be used as well as particlesizes. Lapping and polishing may be done in multiple steps of varyingparticle sizes to achieve the desired surface roughness.

Chemical mechanical polishing may be done with particles having theformula AO.xZ₂O₃, wherein A is at least one divalent cation, Z is atleast one trivalent cation and 0.01≦x≦100. Cations include, but are notlimited to, magnesium, iron (II), zinc, manganese, nickel, calcium andmixtures thereof. Z cations include, but are not limited to, aluminum,iron (III), chromium, titanium and mixtures thereof. Such particles havea specific area of 5 m²/g to 200 m²/g and a mean crystalline diameter of5 nm to 500 nm and a mean aggregate particle diameter of 10 nm to 5000nm. The Zeta potential may be positive, zero or negative. Typically theZeta potential of the slurries are greater than or equal to +10 mV orless than or equal to −10 mV. The aqueous slurry includes particles inamounts of 0.1 wt % to 10 wt %. In addition to the particles, the slurryalso may include oxidizing and reducing agents such as hydroxylaminecompounds ammonium persulfate, hydrogen peroxide, polyelectrolytes andorganic acids. Chelating agents as well as surfactants, stabilizers,suspending agents, buffers and lubricants also may be included.Additional cations also may be included such as, but not limited to,zirconium, copper, cobalt, lithium and rare earth cations.

Other abrasive particles which may be used include, but are not limitedto, diamond, boron carbide, boron nitride, carbon nitride, siliconcarbide, silicon nitride and mixtures thereof. Particle sizes may rangefrom 0.005 microns to 30 microns, or such as from 0.05 microns to 20microns, or such as from 0.5 microns to 10 microns. When diamond pasteis used the particles sizes may range from 2 microns or less, typically1 micron or less. Such abrasive particles may compose 1 wt % to 30 wt %of slurries. Conventional additives such as chelating agents, buffersand surfactants may be included in the slurries in conventional amounts.

Other forms of abrasive treatment include, but are not limited to, fixedabrasive grinding and grit blasting, such as sand blasting. Fixedabrasive grinding typically involves using diamond, silicon carbide andother abrasives which have a Mohs hardness of 9 and higher. Combinationsof such materials also may be used. The abrasive may be in particle formor in the form of a grinding wheel such as a diamond wheel. The surfacespeed of the wheel is at least 1000 m/min., or such as from 2000 m/minto 10,000 m/min. Particles are applied at pressures of 10 psi to 100psi, or such as from 20 psi to 80 psi. Conventional grinding apparatusmay be used.

When grit blasting is used, conventional sand blasting apparatus,particle blast apparatus and blast cabinets may be used. Abrasivesinclude, but are not limited to, diamond, silicon carbide, siliconnitride, boron nitride, boron carbide and combinations thereof.Abrasives are applied to the surface of the articles at pressures of 10psi to 500 psi, or such as from 25 psi to 150 psi. Such pressures areapplied until the desired surface is obtained.

Coatings of materials also may be used to provide the desired surfaceroughness. Such coatings include, but are not limited to, siliconcarbide, silicon, silicon nitride, silicon dioxide and carbon. Suchcoatings may be deposited on the ceramic article surfaces by CVD or PVD.Conventional reactants may be used to form the coatings. Depositiontemperatures and pressures may vary depending on the type of coating.Typically, furnace temperatures may range from 1000° C. to 1500° C., orsuch as from 1200° C. to 1400° C. Furnace pressures may range from 20torr to 760 torr, or such as from 80 torr to 125 torr. Coatingdeposition rates may range from 0.01 microns/min to 5 microns/min orsuch as from 0.5 microns/min to 3 microns/min. Coating thicknesses mayrange from 0.01 microns to 10 microns, or such as from 0.1 microns to 5microns.

The methods described above are exemplary of processes which enable theformation of silicon carbide wafer holding articles which may be used toprocess wafers having reduced slip as well as an improved balancebetween sticktion and float.

Any type of semiconductor wafer may be processed in the wafer holdingapparatus. Typically, the semiconductor wafers are composed of materialswhich include, but are not limited to, silicon, sapphire, galliumarsenic, or silicon carbide. More typically, the semiconductor wafersare composed of silicon. One or more wafers may be processedsimultaneously. The wafers rest in the wafer holding apparatus such thatthe smoothed surface of the wafer holding apparatus contacts from 5% to80% of the wafer surface, or such as from 20% to 70% of the wafersurface to reduce slip and balance sticktion and float. Further, thesurface parameters described above provide no sharp features which mayencourage slip formation. Typically the backside of the wafer rests onthe wafer holding article, which is typically a susceptor ring. Hightemperatures during wafer processing typically cause the wafer to bow orform a convex backside near the center where the wafer is not supportedby the wafer holding article. Although the degree of bowing is only afew microns, there is sufficient bowing which causes the wafer to rubagainst the edges of the wafer holding article on which it rests tocause damage to the wafer when the edges are rough. Such damage may becrystalline point defects, line defects and fractures. To prevent orreduce damage to the wafer during bowing, the edges of the wafer holdingarticles have an edge radius of 0.05 mm or more.

FIGS. 1, 2 and 3 are an example of one type of susceptor ring. As shown,the susceptor ring 10 is used to support a semiconductor wafer 12 duringvarious fabrication processes. The susceptor 10 is formed of two basiccomponents, a ring 14 and a blocker 16. The ring 14 is an annular memberhaving upper and lower faces 18 and 20, respectively. The ring alsoincludes two shoulders formed at the inner side wall 22, designated aswafer shoulder 26 and blocker shoulder 28. Wafer shoulder 26 opens ontothe upper face 18, while the blocker shoulder 28 opens onto the wafershoulder. The seat 30 and back wall 36 join at edge 33.

The wafer shoulder includes a planar seat 30 extending normal to thelongitudinal axis of the ring, and a tubular back wall 32 coaxial withthe longitudinal axis. The back wall 32 intersects the upper face 18. Ina similar manner the blocker shoulder includes a seat 34 and a back wall36, with the back wall 36 of the blocker shoulder intersecting the seat30 to form edge 33. The radius “r” of edge 33, as measured from point“q”, which is at the quarter point from the periphery of the edge, is0.05 mm or more. As shown the seats provide support against gravity forthe wafer and blocker, while the back walls provide support againstgravity for the wafer and the blocker, while the back walls providesupport against movement of the wafer or blocker laterally. In each casethe diameter of the back wall is greater than that of the wafer orblocker, respectively, to permit these items to be easily inserted in,and removed from, the ring. Further, the seats are spaced a distancegreater than the thickness of the blocker, such that there is a spacebetween the bottom face of the wafer and the top face of the blocker, asshown in FIG. 2.

Wafer holders may be used in various wafer processing methods. Suchmethods include, but are not limited to, batch processing chambers, suchas, high temperature annealing of wafers, high temperature diffusion,nitride deposition, single wafer processing chambers, such as, epitaxialsilicon growth, chemical vapor deposition film growth, wafer annealing,high temperature diffusion and plasma etch.

The semiconductor wafers may be processed in the wafer holding articlesin any suitable wafer processing chamber as well as any suitable method.Such methods include, but are not limited to, annealing, diffusion andnitride deposition, epitaxial growth, CVD film growth and plasma etch.Such processes modify the surface of the semiconductor wafer such thatthey may be used in electronic devices.

Examples of annealing include, but are not limited to, adiabaticheating, thermal flux and isothermal heating. Adiabatic involvesapplication of energy provided by a pulse energy source (such as alaser, ion beam, electron beam) for a very short duration of 10 to100×10⁻⁹ seconds. This high intensity, short duration energy melts thesurface of the semiconductor, to a depth of 1 to 2 microns. Thermal fluxinvolves applying energy for 5×10⁻⁶ to 2×10⁻² seconds. Thermal fluxheating creates a substantial temperature gradient extending more than 2microns below the surface of the wafer, but does not cause anythingapproaching uniform heating throughout the thickness of the wafer.Isothermal heating involves energy applied for 1 to 100 seconds to causethe temperature of the wafer to be uniform throughout its thickness atany given region.

Annealing processes may be done in conventional furnaces or in a rapidthermal annealing (RTA) system. The rapid thermal annealing of, forexample, silicon may be carried out in any of a number of commerciallyavailable RTA furnaces in which wafers are individually heated by banksof high power lamps. RTA furnaces are capable of rapidly heating asilicon wafer from room temperature to 1200° C. in a few seconds. Onesuch commercially available furnace is the model 610 furnace availablefrom AG Associates (Mountain View, Calif.).

Epitaxial layers may be deposited or grown on a semiconductor wafer bymany different processes well known in the art. Typically, growth of anepitaxial layer is achieved by chemical vapor deposition. Generally,chemical vapor deposition involves the introduction of volatilereactants, such as SiCl₄, SiHCl₃, SiH₂Cl₂ or SiH₄, with a carrier gas,such as hydrogen, into an epitaxial reactor. Although the processconditions may vary, in the case of monocrystalline layer deposition thetemperature generally ranges from 1080° C. to 1150° C. In addition, theenvironment in which the deposition occurs is typically free ofparticulate contaminants.

Film forming on a semiconductor wafer may be done by thermal chemicalvapor deposition. Typically the process is performed in a single-waferdeposition chamber. For example, in the deposition chamber, ahexachlorodisilane source gas is mixed with an oxidation source gas suchas nitrous oxide to form a silicon oxide film. Alternatively, thehexachlorodisilane source gas is mixed with a nitridation source gassuch as ammonia to from a silicon nitride film. Alternatively, thehexachlorodisilane source gas is mixed with an oxidation source gas suchas nitrous oxide and a nitridation source gas such as ammonia to form asilicon-oxynitride film. The films are formed in the chamber with totalpressure from 10 torr to 350 torr and with a temperature ranging from500° C. to 800° C. The films are formed with deposition rates of 45Å/min to 2000 Å/min. The films formed using hexachlorodisilane may havethicknesses of less than 300 Å and greater than 10 Å.

The modified semiconductor wafers may be measured for slip using anysuitable method known in the art. Measuring slip is not methoddependent. One method used in the industry is to measure and recorddepolarization of incident polarized light after its transmissionthrough the wafer. This may be done with a depolarization imager such asan SIRD™ scanning infrared depolarization tool. Another method ofmeasuring slip in the industry is by stationary beam technology (SBT),which is a laser-based inspection technique. This may be done by using asurface inspection system such as a Surfscan® SP1 unpatterned surfaceinspection system.

The following examples further illustrate the invention, but are notintended to limit the scope of the invention.

EXAMPLE 1

A CVD silicon carbide susceptor ring was machined to a surface roughnessof Ra=0.8 microns using a conventional grinding apparatus. The surfaceroughness was measured using a contact profilometer. The machining wasdone with a diamond wheel initially having a 150 grit followed by adiamond wheel having a 320 grit. Grinding was done at a rate of 1750 rpmfor 9 hours. A photograph of the surface of the susceptor was taken. Thetop portion of FIG. 4 shows a 30× magnification of a portion of themachined surface of the susceptor. FIG. 4 shows the characteristicgrooves and ridges produced by conventional machining.

The susceptor ring was then lapped using a Pellon Pad™ lapping pad usingdiamond paste with a particle size of 4 microns to 8 microns. Lappingwas done for 2 hours at a surface speed of 600 m/min.

A photograph of a portion of the surface of the susceptor was thentaken. The lower portion of FIG. 4 shows a 30× magnification of thelapped susceptor. The grooves and ridges characteristic of conventionalmachining were removed. A smoother surface was obtained.

The surface roughness was measured using a contact profilometer. The Ravalue was determined to be 0.1 microns and the Rz(din) was determined tobe 1 micron. The lapping method provided a surface with a lower Ra valuethan the conventional machining process.

The susceptor ring was then placed in a wafer boat and a semiconductorwafer was placed in the susceptor ring. The wafer boat was then placedin a conventional CVD furnace. The furnace was heated to a temperatureof 1100° C. and an inert argon and hydrogen atmosphere was created asfor epitaxial film formation. The wafer boat with the wafer was heatedin the furnace for 6 hrs. The furnace was then cooled to roomtemperature, and the wafer boat with the susceptor ring and the waferwere removed from the furnace.

Stationary beam technology using the Surfscan® SP1 was used to measurethe slip. The measurements showed no slip. Thus, the lapping methodprovided a susceptor which prevented slip.

EXAMPLE 2

A CVD silicon carbide susceptor ring is machined to a surface roughnessof Ra=0.8 microns using a conventional grinding apparatus and method asdescribed in Example 1. The surface roughness is measured using acontact profilometer.

The susceptor ring is then lapped using a Pellon Pad™ lapping pad usingdiamond paste with a particle size of 4 microns to 8 microns. Lappingwas done for 2 hours at a surface speed of 1200 m/min. The susceptor wasthen polished for 3 hours using a diamond paste having a particle sizeof 2 microns to 4 microns. The Ra is expected to be less than 0.05microns and the Rz(din) is expected to be less than 0.5 microns, asmeasured with a contact profilometer.

The susceptor ring is then placed in a wafer holding apparatus and asemiconductor wafer is placed in the susceptor ring. The apparatus isthen placed into a CVD furnace with an inert argon atmosphere. Thetemperature of the furnace is raised from room temperature to 1100° C.The apparatus is heated in the furnace for 10 hrs. The furnace is thencooled to room temperature. When the wafer holding apparatus reachesroom temperature, it is removed from the furnace. The silicon wafer isremoved from the apparatus, and the amount of slip is determined. Nomeasurable slip is expected.

EXAMPLE 3

A CVD silicon carbide susceptor ring is machined to a surface roughnessof Ra=0.8 microns using a conventional grinding apparatus as describedin Example 1. The surface roughness is measured using a contactprofilometer.

The susceptor ring is then lapped using a Pellon Pad™ lapping pad usingdiamond paste with a particle size of 4 microns to 8 micron. Lapping isdone for 3 hours at a surface speed of 1500 m/min. The susceptor is thenpolished for 4 hours using a diamond paste with particles having a sizerange of 0.25 microns to 1 micron. The Ra is expected to be 0.005microns and the Rz(din) is expected to be 0.05 microns. The edge radiusof the susceptor is expected to be greater than 0.1 mm.

The susceptor is then placed in a wafer boat. A silicon semiconductorwafer is placed in the susceptor boat, and the boat is then placed in afurnace. The furnace is provided with an inert atmosphere of argon andhydrogen. The furnace is heated to 1200° C. and the boat remains in thefurnace for 10 hours. The temperature of the furnace is allowed to coolto room temperature. After the boat with the susceptor ring reaches roomtemperature, the slip is measured using stationary beam technology usinga Surfscan® SP1. No measurable slip is expected.

EXAMPLE 4

A CVD silicon carbide susceptor ring was machined according the sameprocedure as in Example 1 to achieve an Ra=0.8. The susceptor was thenplaced into a standard thermal open air furnace containing 20% oxygen.The temperature of the furnace was raised to 1000° C. and the pressurewas maintained at 1 atmosphere. The susceptor was heated in the furnacefor 12 hours to produce a silicon dioxide layer on the surface of thesusceptor 0.1 microns thick.

The susceptor was then placed in a wafer boat. A semiconductor wafer isplaced in the susceptor and the boat was then placed into a furnace withan inert argon and hydrogen atmosphere. The furnace was heated to 1200°C. The boat was heated in the furnace for 10 hours. The temperature ofthe furnace was then allowed to cool to room temperature. After the boatwith the susceptor ring and wafer reached room temperature, the slip wasmeasured by stationary beam technology using a Surfscan® SP1. Nomeasurable slip was detected.

EXAMPLE 5

A CVD silicon carbide susceptor ring was machined to a Ra=0.8 asdescribed in Example 1. The susceptor ring was then placed in a standardthermal open air furnace to produce a 0.8 microns thick layer of silicondioxide over the ring's surface.

The temperature of the open air furnace was maintained at 1100° C. for200 hrs to produce the silicon dioxide layer over the surface of thesusceptor ring. The furnace was then cooled to ambient temperature. Whenthe sesceptor ring cooled, it was immersed in a 1N hydrofluoric acidsolution for 30 min to strip the silicon dioxide layer from thesusceptor. The temperature of the hydrofluoric acid solution was at 30°C. during stripping.

The surface roughness of the susceptor was measured with a contactprofilometer. The Ra was measured to be 0.1 microns and the Rz wasmeasured to be 1 micron.

The susceptor ring was placed in a wafer boat and a siliconsemiconductor wafer was placed in the ring. The boat was then placedinto a furnace and heated to a temperature of 1050° C. The boat was leftin the furnace for 5.5 hrs in an atmosphere of argon and hydrogen. After5.5 hours the furnace was cooled to room temperature. When the boatreached room temperature, it was removed from the furnace. The wafer wasremoved from the boat and the amount of slip was measured using aSurfscan® SP1 unpatterned surface inspection system. The measurementsshowed no measurable slip.

EXAMPLE 6

A sintered silicon carbide susceptor is machined to a surface roughnessof Ra=1 micron using a conventional machining apparatus. The machiningis done by the same method as described in Example 1. The susceptor isthen polished using a polishing pad and diamond particles having anaverage particle size of 0.5 microns to 1 micron. Polishing is done over5 hours with a surface speed of 2400 m/min.

After the susceptor is polished, it is placed in a conventionalinductively coupled plasma reactor. The temperature of the plasma ismaintained at 1400° C. with a pressure of 10⁻⁵ torr during etching.Hydrogen chloride gas is introduced into the chamber at a rate of 1000ml/min. Etching is done for 60 sec. The Ra is expected to be less than0.5 microns and the Rz(din) is expected to be less than 5 microns. Theradius of the edge is expected to be 0.5 mm. Surface measurements aredone with an optical profilometer.

The susceptor containing a silicon wafer is then placed in a siliconcarbide wafer boat. The wafer is then annealed in a furnace with ahydrogen atmosphere at 1200° C. for 1 hr. The wafer is then annealed ina dry oxygen atmosphere for 1 hr. at 1200° C. The furnace is allowed tocool to room temperature. After the wafer cools to room temperature itis removed from the suceptor. The wafer is not expected to show any slipas measured by either an SIRD™ or a Surfscan® SP1.

EXAMPLE 7

A sintered silicon carbide susceptor ring is machined to a surfaceroughness of Ra=2 microns using a conventional grinding apparatus.Grinding is done by the same method as in Example 1 except that grindingis done for 6 hours instead of 9.

The susceptor is placed in a helicon plasma etch reactor. Thetemperature of the reactor is held at 1200° C. with a pressure of 10⁻⁵torr during etching. Nitrogen fluoride is fed into the reactor at a flowrate of 500 ml/min as a source of fluorine gas. Etching is done for 30min. The reactor is then allowed to cool to room temperature and whenthe susceptor reaches room temperature it is removed from the chamber.

The surface of the susceptor is then treated with a mixture of mineralacids containing 50 wt % hydrofluoric acid and 50 wt % nitric acid. Thesusceptor is immersed in a bath of the acid mixture for 20 sec. Thetemperature of the solution is 35° C. The susceptor is expected to havean Ra of 0.5 microns and an Rz(din) of 3 microns. The edge radius isexpected to be 0.1 mm.

A silicon wafer is placed on the susceptor. They are placed in a furnacewith an argon atmosphere and heated for 10 hr at 1400° C. Thetemperature in the furnace is reduced to room temperature. When thesusceptor and wafer reach room temperature, they are removed from thefurnace. The wafer is expected to show no measurable slip by using aSurfscan® SP1 and an SIRD™.

EXAMPLE 8

A CVD silicon carbide susceptor ring is machined by the same method asdescribed in Example 1. The suceptor ring is then placed in a heliconplasma reactor. Hydrogen gas is added to the reactor at a flow rate of50 ml/min and chlorine gas is added to the reactor at a rate of 300ml/min. Neon gas is added to the chamber at a rate of 100 ml/min toprovide an inert atmosphere in the reactor. The temperature in thereactor is held at 1500° C. with a pressure of 10⁻⁸ torr. Etching isdone over 60 min. The susceptor is expected to have an Ra of 0.5 micronsand an Rz(din) of 3 microns. The edge radius is expected to be 0.25 mm.

The susceptor with a silicon wafer is placed into a reactor which has ahydrogen atmosphere. The temperature of the reactor is 1300° C. Thewafer is treated for 3 minutes. The surface of the wafer is then etchedwith 65% by volume of gaseous hydrogen chloride. The pressure in thereactor is at 2 torr.

After the wafer is etched, silicon layers are grown on the wafer usingdichlorosilane and hydrogen are the reactants. The reaction mixture is60% by volume of dichlorosilane and 40% by volume of hydrogen. Thetemperature of the reactor is reduced to 1050° C. during silicon growth.The pressure is maintained at 2 torr. Growth rate is 0.2 to 0.3 micronsper min.

When the wafer cools to room temperature, it is removed from thereactor. The wafer is expected to show no measurable slip defects usingthe SIRD™ or Surfscan® SP1 instruments.

EXAMPLE 9

A CVD silicon carbide susceptor ring is machined and lapped to a surfaceroughness of Ra=0.1 microns and an Rz(din)=1 micron as described inExample 1. A silicon wafer is then placed on the ring and both areplaced in a single-wafer deposition chamber.

The deposition temperature for forming a film on the silicon wafer is800° C. and the pressure in the chamber is 50 torr. The reactants areammonia gas supplied at a rate of 50 ml/min and hexachlorodisilanesupplied at a rate of 60 ml/min. Film deposition occurs at a rate of 0.2to 0.3 microns per min.

After a silicon nitride film is formed on the silicon wafer, it isallowed to cool to room temperature in the chamber. No measurable slipis expected to be detected on the wafer using the SIRD™ or Surfscan® SP1instruments.

EXAMPLE 10

A chemical vapor deposited silicon carbide susceptor ring was machinedto a surface roughness of Ra=0.8 microns using a conventional grindingapparatus and method as described in Example 1. The surface roughnesswas measured using a contact profilometer.

The susceptor ring was next sandblasted using a silicon carbide powderwith a mesh (grit) size of 400. The silicon carbide powder was blastedthrough a tungsten carbide nozzle with a diameter of ⅛ inch at apressure of 100 psi. The entire surface of the susceptor ring wassandblasted until all machining marks were no longer visible on thesurface and the surface had a uniform appearance. The entiresandblasting operation takes approximately 30 minutes to complete.

The surface roughness was measured using a contact profilometer and theaverage roughness was Ra=1.9 microns and Rz(din)=7.6 microns.

The susceptor ring was then placed in a wafer boat. A silicon wafer wasplaced on the susceptor ring and the boat was then placed into a furnacewith an inert argon and hydrogen atmosphere. The furnace was heated to1200° C. The boat was heated in the furnace for 10 hours. Thetemperature of the furnace was then allowed to cool to room temperature.After the boat with the susceptor ring and wafer reached roomtemperature, the slip was measured. No measurable slip was detected onthe silicon wafer using the SIRD™ or Surfscan® SP1 instruments.

EXAMPLE 11

A chemical vapor deposited silicon carbide susceptor ring was machinedto a surface roughness of Ra=0.8 microns using a conventional grindingapparatus and method as described in Example 1. The surface roughnesswas measured using a contact profilometer.

The susceptor ring was next sandblasted using a silicon carbide powderwith a mesh (grit) size of 400. The silicon carbide powder was blastedthrough a tungsten carbide nozzle with a diameter of ⅛ inch at apressure of 100 psi. The entire surface of the susceptor ring wassandblasted until all machining marks were no longer visible on thesurface and the surface had a uniform appearance. The entiresandblasting operation takes approximately 30 minutes to complete.

The susceptor ring was next sandblasted using a silicon carbide powderwith a mesh (grit) size of 1000. The silicon carbide powder was blastedthrough a tungsten carbide nozzle with a diameter of ⅛ inch at apressure of 120 psi. The entire surface of the susceptor was sandblastedfor about 20 minutes.

The surface roughness was measured using a contact profilometer and theaverage roughness was Ra=1.3 microns and Rz(din)=5.5 microns.

The susceptor ring was then placed in a wafer boat. A silicon wafer wasplaced on the susceptor ring and the boat was then placed into a furnacewith an inert argon and hydrogen atmosphere. The furnace was heated to1200° C. The boat was heated in the furnace for 10 hours. Thetemperature of the furnace was then allowed to cool to room temperature.After the boat with the susceptor ring and wafer reached roomtemperature, the slip was measured. No measurable slip was detected onthe silicon wafer using the SIRD™ or Surfscan® SP1 instruments.

What is claimed is:
 1. A wafer holding article comprising a surfaceroughness of Ra less than or equal to 3 microns and an Rz(din) of lessthan or equal to 15 microns, wherein the wafer holding article has anedge radius of 0.1 mm to 1 mm.
 2. The wafer holding article of claim 1,wherein the surface has a silicon dioxide coating of 0.5 microns to 5microns.
 3. The wafer holding article of claim 1, wherein the waferholding article is silicon carbide.
 4. The wafer holding article ofclaim 1, wherein the surface roughness of Ra is from 0.1 microns to0.001 microns.
 5. The wafer holding article of claim 4, wherein thesurface roughness of Ra is from 0.01 microns to 0.005 microns.
 6. Thewafer holding article of claim 1, wherein the Rz(din) is from 1 micronto 0.005 microns.
 7. The wafer holding article of claim 1, wherein theRz(din) is from 3 microns to 0.05 microns.